This invention relates generally to archery equipment and more specifically to crossbow type devices.
The crossbow is an ancient weapon that has remained relatively unchanged over the centuries and up to modern times. The crossbow has a number of advantages over the traditional or conventional archery bow configuration. One such advantage is that the crossbow uses a stock that allows the device to be supported, aimed and fired using a trigger much in the same manner as a rifle. Yet another advantage that a crossbow provides is that the bowstring is mechanically held in the fully drawn position eliminating the need for the archer to physically hold the fully drawn bowstring while aiming and shooting the device. These two advantages are among the primary reasons that the crossbow is sometimes chosen over the traditional bow configuration. Another aspect of the crossbow that is often mistaken for an advantage is that the crossbow utilizes a much higher poundage draw weight than the regular bow, leading some to believe that the that the crossbow must be a more efficient and more powerful weapon than the bow.
In reality, however, even in the case of the more modern versions of the crossbow where compound bow type limb mounted cams are used in order to increase the stored energy, this is not the case. The dimensional limitations of the conventional crossbow restrict the power stroke to a very short length as compared to a bow. In order to compensate for the relatively short power stroke, an extremely high draw weight must be used in order for the crossbow to obtain projectile velocity that approaches or is equal to the arrow velocity obtained from a conventional bow. Further, the necessity to employ such high draw weight dictates that the projectile take the form of a very rigid, strong and heavy object commonly known as a bolt as opposed to an arrow which can be more closely matched in terms of weight and spine to the draw weight in order to optimize efficiency. Thus the crossbow is, comparatively, a much less efficient device than the bow. Subsequently, the requirement of an extremely high draw weight, in many cases, makes the crossbow either undesirable or even unusable for a number of archers due to the difficulty encountered in drawing and cocking the device. Although a number of unique devices have been developed to assist in drawing and cocking the heavy pull weight of a crossbow, such devices are normally cumbersome, elaborate, tedious, or equally uncomfortable and inconvenient to use.
Some modern versions of the crossbow utilize limb mounted cams similar to those used on compound bows in order to improve the energy storing capability of the device relative to the power stroke restrictions and draw length requirements. In addition, some examples utilize the cams and axle-to-axle length to increase the power stroke, which has improved performance to a degree. However, using limb mounted cams on a crossbow in the same manner that they are used on a conventional compound bow introduces the same undesirable conditions such as limb twist, cam lean, and asymmetrical loading to the projectile as well as various components that occur with conventional compound bow design.
In order to compensate for the inherent inefficiencies of the conventional compounding system along with an increased mass at the limb tips, the highest draw weight possible must be used. However, although the draw weights used are substantially in excess of that of a compound bow, it is usually impractical to design the components of a compound type crossbow such that they would withstand the somewhat higher forces that may be used with traditional, re-curve limb type crossbows. This usually makes the traditional, re-curve type crossbow actually faster and, in view of the absence of the inherent inefficiencies of the conventional compounding system, more efficient. Of course, the higher poundage of the traditional crossbow that is dictated by the short power stroke, again, makes such a configuration undesirable in many cases.
Due to the dynamic forces applied to the bolt (projectile) used with the common crossbow, the common method of supporting the bolt at full draw is that of a channel or groove deployed along the upper portion of the barrel in which the bolt rests with a positioning groove in the riser to center the bolt in the channel and a spring type finger to hold the rear of the bolt in place near the fletching. While this means of supporting the bolt in a crossbow is necessary, it also lends to the inefficiency of the device to a degree in that a lengthy duration of contact between the bolt and the barrel is experienced during launch.
Therefore, it can be easily recognized that it would be most desirable to create a modern crossbow type device that possesses the most desirable features of the crossbow such as a configuration that utilizes a rifle type stock to facilitate supporting, aiming, and shooting the weapon and the feature of mechanically cocking, holding and releasing the bowstring using a trigger mechanism, while providing the power, accuracy and efficiency of a compound bow without the requirement for excessively high draw weight and without the inherent efficiency and accuracy problems that exist with conventional compound bow systems.
A relatively new form of compound bow designed to eliminate the problems associated with conventional compound bow design relative to efficiency, accuracy performance, lack of versatility, and other aspects is shown in my U.S. Pat. No. 7,047,958, the disclosure of which is incorporated herein by reference.